Mycosis fungoides is a rare cutaneous T-cell lymphoma of unknown etiology, affecting two persons per million per year. Several clinical and anecdotal reports have suggested that phenoxyherbicide exposures may substantially increase risk for this neoplasm. In fact, of the white mycosis fungoides patients seen at the University of California Medical Center during 1976-1981, 90% had hispanic surnames and were residents of the agricultural growing areas of California. We propose a case-control study of mycosis fungoides to include 160 newly diagnosed patients and 320 controls who reside in the 45-county Northern California region. Structured personal interviews will be conducted with subjects by telephone. The information requested from subjects will permit testing of hypotheses relating mycosis fungoides risk to 1) occupational exposures to phenoxyherbicides, pesticides, and chemicals associated with the petrochemical industry; 2) employment in one of the following industries: electrical, construction, textile manufacturing, rubber manufacturing, painting, printing, machinery operation; 3) allergies, illness and other familial and lifestyle factors. The proposed study has the following advantages: 1) Stanford and the University of California Medical Centers are major referral centers for mycosis fungoides in the western United States, treating 50-60 newly diagnosed patients each year; 2) The Northern California Cancer Program facilitates rapid and complete ascertainment of all cases reported to the five-county San Francisco-Oakland SEER tumor registry; 3) Unlike an occupational cohort study, a case-control study will amass adequate patient numbers to detect plausible relative risks associated with the hypothesized exposures; 4) The 45-county Northern California region makes it an excellent location to evaluate exposures to the chemicals of interest. This region has long-term, extensive use of phenoxyherbicides for forestry management and roadside brush control; a high agricultural industry with widespread pesticide application; and a large petrochemical industry in Contra Costa County.